B3.2.6 + B3.2.7 - Plant Hormones

Question 1

What is a tropism?

Answer 1

Growth in response to an external stimulus

Question 2

What is phototropism?

Answer 2

Growing towards the light

Question 3

Why is it beneficial for a plant to grow towards the light.

Answer 3

When a stem grows towards the light, the plant can photosynthesis more. This means more food is produced for the plant so it can grow faster.

Question 4

What is gravitropism?

Answer 4

Growing in the same direction as gravity.

Question 5

Why is it important for the roots to grow downwards

Answer 5

The soil helps provide anchorage. It normally takes the roots nearer to water
It ensures the plant grows correctly

Question 6

Where is auxin made

Answer 6

Near the tips of plant shoots and roots.

Question 7

How do plants respond to their environment?

Answer 7

The response to a stimulus occurs because of an uneven distribution of auxin.
This causes an unequal growth rate which results in the shoot or root bending.

Auxin stimulates the shoot cells to grow more but inhibits the growth of root cells.

Question 8

How do plants respond to light?

Answer 8

• When light hits one side of a shoot tip, the auxin moves to the other side of the shoot.
• This causes the concentration of auxin to build up in the unlit side
• the cells respond by elongating. This increases the length of this side of the shoot, so the shoot bends towards the light.

Question 9

Why do some plants grow straight?

Answer 9

Because auxin is evenly distributed on the tip

Question 10

What do auxins do?

Answer 10

They stimulate growth by causing cell elongation.

They also help to regulate fruit development.

Question 11

What does ethene do?

Answer 11

It causes fruits to ripens by stimulating the conversion of starch into sugar.
It is the only plant hormone to exist as a gas

Question 12

What do gibberellins do?

Answer 12

They promote growth, particularly stem elongation. They also end the dormancy of seeds.

Question 13

What are commercial uses of plant hormones?

Answer 13

Killing weeds
Promoting root growth
Delaying ripening 
Ripening fruit
Producing seedless fruit
Controlling dormancy

Question 14

How are hormones used to kill weeds?

Answer 14

• Many weed killer contain AUXINS.
• weed killers are selective herbicides. They kill weeds that are broad leaved plants but do not affect narrow leaved plants.
• the auxin makes the weeds grow too fast which kills the weed.

Question 15

How are hormones used to promote root growth?

Answer 15

Auxin.

Rooting powders contain auxin.

Question 16

How are hormones used to delay ripening?

Answer 16

Auxin is sprayed on fruit trees to delay ripening.

-thus prevents fruit from dropping off trees early so that the harvest can be collected at the same time.

Question 17

How are hormones used to ripen fruit

Answer 17

ETHENE is sprayed on fruit trees and plants so that their fruits ripen quicker. This allows fruit to be ready earlier in the growing season

Question 18

How are hormones used to produce seedless fruit?

Answer 18

If AUXINS are applied to unpollinated flowers the plant produces seedless fruit.

Question 19

How are hormones used to control dormancy

Answer 19

They are sprayed with gibberellins

Question 20

Why do gardeners take cuttings?

Answer 20

To make copies of successful plants

Question 21

Why can’t identical clones of a plant be made?

Answer 21

Because of environmental variation